Over the past few months, a Russian political scientist named Valery Solovei has stoked a global frenzy with a sensational claim: that Vladmir Putin died last year and today is represented in public by a body double. The Kremlin’s elite, Solovei tells his half-million online followers, controls the double and has stuffed Putin’s body in a freezer. Then on Thursday, journalist Tucker Carlson aired a two-hour interview with Putin. Solovei shrugged it off as a sham. Carlson, he said, interviewed Putin’s doppelgänger, who will now be passed off as real to millions of viewers in the West. “Putin is dead,...